1. Field of the Invention:
The invention generally relates to a mechanism for controlling the speed of a heavy duty output shaft, hereinafter referred to simply as a heavy duty shaft. More precisely, the invention relates to a speed control device particularly suited for use in mechanically limiting the speed of a heavy duty shaft to the speed of a small shaft, hereinafter referred to as a reference speed shaft, driven at a precisely controlled reference speed.
2. Description of the Prior Art:
It is contemplated that for certain future space missions extensive use will be made of solar sails in propelling spacecraft through celestial space environments. As a consequence, it is further contemplated that because of an increased use of solar sails reliance upon rocket engines and the like for propulsion purposes greatly will be reduced.
One of the various types of systems currently proposed for use includes a plurality of deployable blades adapted to assume an extended configuration in response to angular momentum imparted thereto in reponse to angular displacement of a common supporting element. Each of the blades, when extended, is approximately eight meters wide and 6,250 meters long. Therefore, it is further proposed that the blades be furled about a rotatable element for facilitating launch and subsequently unfurled into an extended configuration. Consequently, large torques can be expected to be encountered as the blades are unfurled in response to centrifugal forces acting thereon. Consequently, the speed at which the supporting element is driven in achieving an unfurling of the blades must be precisely controlled in order to avoid an introduction of unbalancing radial forces resulting from uneven mass distribution to the blades.
The prior art, of course, is replete with brakes and the like which, in operation, serve to control the speed or angular velocities of driven elements and shafts of various sizes and configurations. For example note U.S. Pat. No. 2,234,181 to Walter T. Lang. However, the speed control devices heretofore employed in controlling the angular velocity of heavy duty shafts generally lack the required precision to be found acceptable in environments wherein weight, bulk and power limitations are of a primary concern, such as in those instances in which the devices are to be employed in a celestial space environment.
It is therefore the general purpose of the instant invention to provide a novel speed control device for a heavy duty shaft characterized by a reference speed shaft coupled in driven relation with a small precisely controlled stepper motor adapted to impart thereto an angular velocity to which the angular velocity of the heavy duty shaft is continuously compared mechanically and a brake for controlling the angular velocity of the heavy duty shaft for limiting its speed to that of the reference speed shaft.